MPs will be recalled to Parliament for a debate and vote on Syria on Thursday.

David Cameron said there would be a clear Government motion laid before MPs on the UK’s response to the chemical weapons attack on the outskirts of Damascus that left hundreds dead.

The PM returned to Downing Street this morning after cutting short his summer holiday to meet Cabinet colleagues and continue talks with international leaders to find a “proportionate” response which will “deter” the Syrian state from using toxic agents.

He wrote on Twitter: “Speaker agrees my request to recall Parliament on Thurs. There’ll be a clear Govt motion & vote on UK response to chemical weapons attacks.”

The recall comes after Downing Street confirmed Britain's armed forces are drawing up contingency plans for military action.

Syrian President Bashar Assad’s regime has denied “utterly and completely” that it was behind the atrocity and has warned that military action would be a violation of international law and doomed to fail.

No 10 indicated that an agreement on the next steps could be taken before the results of a report by UN weapons inspectors into the attack is produced but insisted that any response would be legal.

“No decision has yet been taken,” a Downing Street spokesman said. “We are continuing to discuss with our international partners what the right response should be, but, as part of this, we are making contingency plans for the armed forces.”

Cabinet ministers, including Defence Secretary Philip Hammond, have arrived at No 10 for talks ahead of a national security council (NSC) tomorrow which will discuss possible UK involvement in using force.

Syrian foreign minister Walid Muallem today denied “utterly and completely'' that state forces had been behind the attack and warned that the nation would defend itself by “all means available''.

At a press conference in Damascus, he said: “They said that the Syrian forces, the Syrian army are the ones who did this attack.

“I deny it utterly and completely.

“There is no country in the world who would use an ultimate destruction weapon against his own people.”

Mr Cameron told world leaders, including US President Barack Obama and Russian President Vladimir Putin, over recent days that the international community “needs to respond” to the “completely and utterly abhorrent and unacceptable” attack, Downing Street said.

A spokesman added: “In terms of end-game, this is about looking at how we deter the use of chemical weapons because this is something that is completely abhorrent and against all international law.

“This is about deterring the use of chemical weapons.”

US Secretary of State John Kerry has said the attack was a “moral obscenity” which “should shock the conscience of the world” and promised action to hold the regime accountable.